Selective liquid phase hydrogenation of citral on Au/Fe2O3 catalysts

Abstract

Gold supported on iron oxide hydrogenates citral (an alpha,beta-unsaturated aldehyde) to the corresponding alpha,beta-unsaturated alcohols (geraniol and nerol) with a selectivity higher than 95%.

Gold supported on iron oxy-hydroxides: a versatile tool for the synthesis of fine chemicals

“…The deposition-precipitation of gold onto the supports was carried out in agreement with the Haruta's procedure [23], by adding 5 g of the support to 400 ml of an aqueous solution containing 5 g of HAuCl 4 . The temperature of the solution was 343 K and the pH was previously adjusted in the range 7-8 by addition of NaOH 0,2 M. Upon addition of the support the pH slightly decreases, then when the equilibrium was reached it was increased up to 7-8 by further addition of NaOH.…”

“…The coprecipitation was carried out using HAuCl 4 (Fluka) and Fe(NO 3 ) 3 ·9H 2 O (Fluka) as starting materials. An aqueous mixture of HAuCl 4 and Fe(NO 3 ) 3 ·9H 2 O was poured into an aqueous solution of Na 2 CO 3 1M (pH=11.9) and kept at 353 K under vigorous stirring. The solids were digested overnight at room temperature and then washed with water until free of chloride ions (AgNO 3 test) and then dried under vacuum at 353 K for one day.…”

“…Ponec et al have reported that the rate of hydrogenation of the C=O bond of propanal is dramatically enhanced by addition of Sn(II), Ga(III) or Fe(III) to a Pt/SiO 2 catalyst, whereas the rate of hydrogenation of acetone is only hardly increased [20]. Selective hydrogenation of ␣,␤ unsaturated ketones to the corresponding unsaturated alcohols, with molecular H 2 , has been instead achieved on Au supported on iron oxyhydroxides catalysts [4][5][6]. In particular, in the hydrogenation of benzalacetone and 4-methyl,3-penten,2-one the selectivity towards the formation of unsaturated alcohol was higher than 60% up to quantitative conversion of the substrates.…”

“…Up to now studies on this topic have been almost unsuccessful [16]. The main routes for the synthesis of unsaturated alcohols from ␣,␤ unsaturated ketones are the classical homogeneous reduction with LiAlH 4 or reduction by hydride transfer to the enone C=O group [17,18].…”

“…Gold supported on iron oxy-hydroxides, hydrogenates, citral and cinnamaldehyde to the corresponding ␣,␤ unsaturated alcohols with a selectivity higher than 85%, without the addition of promoters [3,5].…”